(1) Field of the Invention
The present invention relates to pressure equalization devices and particularly to apparatus for use in pressurizing or depressurizing feed chambers in which material to be delivered to the interior of a shaft furnace is temporarily stored. More specifically, this invention relates to reducing the wear of apparatus employed in the alternate pressurization and depressurization of a chamber, particularly an intermediate storage hopper in a shaft furnace charging installation, and also to reducing the noise level incident to operation of such apparatus. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
(2) Description of the Prior Art
Modern blast furnaces operate with high "counterpressures" in the region of the furnace throat. These throat pressures may reach or exceed a level of 3 kg/cm.sup.2. Efficient operation of such high pressure furnaces dictates that the burden or charge on the furnace hearth be replenished while the furnace is in operation and the charging must be accomplished without there being any appreciable pressure loss. In order to accomplish charging of a modern blast furnace, the materials to be deposited on the hearth may be delivered to and temporarily stored in an intermediate feed hopper which functions as a pressure equalizing chamber. U.S. Pat. No. 3,693,812 discloses a furnace charging installation including two intermediate feed hoppers. These intermediate feed hoppers are alternately isolated from the pressure conditions prevailing within the furnace and the ambient atmospheric pressure by sealing flaps or valves. The intermediate feed hoppers are operated in accordance with a predetermined cycle; i.e., while one of the hoppers is at atmospheric pressure and being filled with charge material the other will be at furnace pressure and will be discharging its contents into the furnace. Before refilling of a previously discharged intermediate feed hopper can be undertaken, the pressure in the hopper must be equalized with the ambient atmospheric pressure. Also, before the contents of a refilled feed hopper may be discharged into the furnace the pressure within the hopper must be equalized with that prevailing in the furnace throat. The requisite pressure equalization is typically accomplished by supplying blast furnace gas at furnace pressure to the intermediate feed hoppers and releasing this gas to the atmosphere as appropriate. The delivery of pressurized furnace gas to a feed hopper at atmospheric pressure and the venting of a pressurized intermediate feed hopper to the atmosphere is accomplished through the use of apparatus including pressure equalization valves. An example of a pressure equalization valve suitable for use with a shaft furnace may be found in U.S. Pat. 3,601,357.
The prior art systems for alternately pressurizing and depressurizing intermediate feed hoppers for blast furnaces which operate at high throat counter-pressures have been characterized by comparatively rapid deterioration of components and a high degree of noise during operation. These two problems, although of a different nature, are both caused by the rapid expansion and consequent large pressure drop of the gases which pass through the pressure equalization valves. The amount of wear suffered and the noise emitted is a direct function of the furnace throat pressure, the volume of the chamber in which the pressure is being equalized and the speed at which the equalization valve is actuated. The trend in blast furnace design is to increase furnace throat counter-pressure and also furnace size, increases in furnace size requiring larger intermediate feed hoppers, and thus the wear and noise problems are becoming aggravated. The solution of these problems has for some time been considered essential to permitting further progress in the development of more efficient blast furnaces.
To further discuss the problems of noise generation and wear in pressure equalization systems, when a pressure equalization valve is opened gases at a pressure which may equal or exceed 3 kg/cm.sup.2 will pass through the valve and will expand downstream thereof. This expansion causes the gases to be accelerated to a speed which may approach or exceed the speed of sound. Wear is caused by entrained particles of dust which impact against metal parts, particularly the conduit walls downstream of the valve, thereby resulting in erosion of these parts. The noise resulting from the expansion of gases through the equalization valve largely occurs in a turbulence zone which forms immediately downstream of the valve.
While the noise resulting from operation of a pressure equalization system may be reduced to an acceptable level through the use of sound insulation materials and silencers, the problem of erosion has not previously been solved. The use of sound insulation material and silencers increases the cost and complexity of the pressure equalization system and the erosion requires periodic servicing for the purpose of replacing worn parts.